[Amps] AL-1200 Pop/Arching, 756 Pro II failure

[Dana Roode]

Bill/Others --

I found that the resister in the copper coil from the plate of the tube 
leading to the tank circuit had indeed come unsoldered.  This may sound 
naive, but would this make an arc?  The coils, taps, etc, look OK.


   Dana


Bill Turner wrote:
> On Fri, 10 Oct 2003 21:40:48 -0700, Dana Roode <K6NR at ARRL.net> wrote:
> 
> 
>>A question for those with AL-1200 repair experience --
>>
>>I bought a used AL-1200 amp a few months ago - it has a low serial number, 
>>108, so I assume its pretty old.  I have used it in several contests and it 
>>has been working well.
>>
>>This weekend we were using it in the California QSO party when there was a 
>>loud pop and an arc visible from the side venting holes, perhaps near the 
>>filter capacitor and rectifier boards.  The Icom 756 PRo II I was driving it 
>>with went south at the same time - no transmit power (received everything 
>>else was fine).  The Pro II is headed back to Icom for repairs.
> 
> 
> _________________________________________________________
> 
> I had a similar experience with my AL-1200 which I bought when they
> first came out.  In fact, it happened twice.
> 
> In the first case, I was running RTTY in a contest and the tank coil
> overheated.  There was a flash and arc and the solder joint for the 80
> meter tap had let go - the tank coil had run hot enough to melt the
> solder!
> 
> In the second case, the solder joint held but the coil got so hot the
> plastic strips it's wound on melted and twisted themselves out of
> shape, accompanied with more arcing.
> 
> You may not have had the exact same problem, but be suspicious of
> anything involving the tank circuit.  Check everything carefully.
> 
> Later on, the tube shorted out and was replaced under warranty, but
> this caused no additional damage.
> 
> Needless to say, this is not a brick-on-the-key amplifier.  I sold it
> and bought an Alpha.  No more problems.
>